This invention relates to an apparatus for measuring certain characteristics of chains, and more particularly to an apparatus for measuring such characteristics of chains commonly used in chain saws.
A particular problem in the maintenance, repair and replacement of chains, particularly of the type utilized in chain saws, is making a proper determination of the physical characteristics of the chain in order that maintenance, repair and replacement may be accomplished. For example, when replacing a particular chain from a chain saw it is necessary to know exactly the number of links which the chain to be replaced has in order that a proper fit of the chain on the chain saw may be accomplished. Heretofore it has been customary to count the number of links by a manual count, usually by marking a starting link and manually counting each link around the chain loop. This method lends itself to inaccuracies, as it is easy to miss a link count or count a link twice. If such an error is made, and a replacement chain is constructed with one or more missing links or additional links, the replacement chain is useless for the purpose intended. Another technique which has been used in attempting to measure the overall length of a chain loop is to lay it on a flat surface and extend it into an elongated form and measure the length from end to end. This technique also leads to inaccuracies, as it is dependent upon the degree of loop elongation while making the measurement, and requires that the loop shape be identical both in the chain to be replaced and in the new chain to be constructed.
Chains are frequently replaced by a dealer who purchases chain in bulk lengths wound around spools. This replacement chain may be withdrawn from the spool to any selected length, and then assembled into a new chain look for replacement purposes. For the reasons described above, it is important that a replacement chain have precisely the same number of links as the chain to be replaced.
In the case of chains in general, and particularly in the case of chains utilized on chain saws, repair, maintenance and replacement is made more difficult by the fact that such chains are available in a number of different link sizes. The size of a chain link is typically referred to as the chain pitch, and chain pitch is commercially available in up to six different link dimensions. The foremost common chain pitches are 0.250 inches, 0.325 inches, 0.375 inches, and 0.404 inches. Since these chain pitch sizes are relatively similar in size dimensions, it is difficult to ascertain with the naked eye precisely which of the several chain pitches one is observing in a particular case. Measurement with a ruler or other linear scale is possible, but even this measurement must be done precisely in order to ascertain the relatively close dimensional tolerances which exist between the various chain pitches.